Draft control



E. T. DAHL DRAFT CONTROL May 28, 1935.

Filed Oct. 7. 19:52

4 Sheets-Sheet l May 28, 1935. i DAHL 2,002,693

DRAFT CONTROL Filed Oct. 7, 1932 4 Sheets-Sheet 2 lave/2601'."

May 28, 1935. E. T. DAHL 2,002,593

DRAFT CONTROL Filed Oct. 7, 1952 4 Sheets-Sheet 5 .Trzbezzior:

May 28, 1935. E. T. DAHL 2,002,693

DRAFT CONTROL Filed Oct. 7, 1952 4 Sheets-Sheet 4 In yen for!" By MQLZWLW WQA liar/a e ya.

Patented May 28, 1935 UNITED STATES PATENT OFFICE mesne assignments, to

wood, Mass.

Frank A. Morrison,

Eldon Macleod, West- Newton,

Mass.; Cameron Macleod, Berwyn, Pa.; Leslie Soule; Dedham, Mass.;

trustees, doing business as Needham, Mass.,

Sullivan A. Sargent, Jr.,

Mason-Neilan Regulator Company, Boston,

Mass.

Application October 7, 1932, Serial No. 636,709.

22 Claims.

This invention relates to control mechanism and more particularly tomechanism for controlling the draft in a furnace in accordance withvariations in external draft conditions and in changes in the amount offuel supplied to the furnace.

This invention is a modification and adaptation of the basic principleof control disclosed in my application, Serial No. 635,356 filedSeptember 29, 1932, for Dual control mechanism, to which reference ishereby made. The invention herein may be classified as rate of flowcontrol of furnace draft and is adapted nace and in stationary furnace,burning both solid and fluid fuels.

The object of the invention is to provide the proper air supply forcomplete combustion at all times. Another'object is to automaticallymain.- tain any desired draft differential between the stack and the airintake duct from the blowers or differential across the boiler tubesthemselves necessary to' insure a high CO2 and a low CO content in thestack gases, and to control this draft differential in accordance withvariations in the supply of fuel to the burner. Thus as the amount offuel is increased and more fuel is burned, the draft control mechanismautomatically increases the amount of air in the proper ratio to thefuel being burned to insure complete combustion. Likewise when less fuelis consumed, the mechanism automatically reduces the air supplied toagain provide complete combustion without excess air. The amount of airsupplied is also varied in accordance with external draft conditions.

As is well known, the natural stack draft varies considerably inaccordance with external draft conditions such as the velocity anddirection of i the wind and the atmospheric pressure. If no draftcontrol mechanism is used, the blowers running at a constant speed willcreate an excessive draft differential whenever the stack draftincreases, as when strong head winds are blowing. With my draft controlmechanism, when external conditions increase the stack draft, theblowers may be run at slower speeds with resulting blower steam savings.My draft control mechanism is sensitive to the slighest variation instack draft and automatically controls the supply of steam to theblowers so as to maintain the desired draft differential at all times. 7

An important advantage of my draft control mechanism is that itdefinitely eliminates the smoke nuisance. As all engineers know, the

presence of smoke belching from a ships stacks for use in marinefurindicates incomplete combustion. Combustibles are passing throughfurnaces and out through the stacks without giving up their energy, andmuch fuel is thereby wasted. Furthermore, in many harbors, fines andother penalties are imposed upon ships for excessive smoking and thesepenalties may be avoided by the use of my draft control mechanism.Hitherto it has been common practice to eliminate the smoke nuisance byexcessive air, and this practice is difficult to detect until the excessair becomes sufficient to create the tell-tale white smoke. Buteliminating the smoke nuisance by use of excessive air is tremendouslycostly in its heat loss. It has been ascertained that an oil firedfurnace temperature with a C02 of 13.7% in the fuel gases (15%indicating perfect combustion) is 3743 F., while with a C02 content of8%, for example, the furnace has a temperature of 2302 F. Thus while theuse of excessive air may avoid smoke, it conceals a heat loss of thefurnace of 1441 F., or almost one third. By means of my draft controlmechanism I am able to maintain the correct draft and air supply inaccordance with variations in external draft conditions and in fuelsupply at 25 all times and eliminate the smoke nuisance without heatloss.

It is impossible to maintain this correct draft differential manuallyexcept with extreme vigilance on the part of ciency of trial runs thefireman. The high cmof steamships, where expert control is provided, isseldom equalled in practice. Accurate indicating instruments must firstinform the fireman what the boiler draft differential is before he canmake the necessary blower speed changes. The fireman must then beconstantly alert to note the stack draft, the blower speeds, the amountof oil, coal, or other fuel passing through the burner, and keeping allthese factors in mind, set the blowers in accordance therewith. Exceptin trial runs, manually controlled blowers are not changed in accordancewith every blower condition as is necessary for maximum economy andefficiency. My mechanism greatly simplifies boiler operation byautomatically providing the correct draft differential in accordancewith varying conditions .which is the most important and mostdiificultpart'of boiler operation.

Briefly, in the fluid fuel burning installationa furnace. The proper,preferably provided by I my mechanism includes draft for the furnace isa steam-driven blqwer mounted on the steam and a control valve is lineto the blower. instrument responsive to rate of flow, such as a. 55

pair of 'sylphon bellows, is placed in the draft passage line of thefurnace, one connection being in the air intake duct and the other atthe stack, so that the instrument moves in accordance with the draftdifferential between the blower and the stack. A second instrument,sensitive to pressure, is placed in the fuel supply line to the burner.The rate of flow and pressure .responsive instruments then operate onthe control valve through an independent pressure system, and throughtheir resultant action to control the supply of steam operating theblower.

In the coal burning installation, the mechanism is the same, except thatcoal is supplied preferably by a steam-operated stoker, and the secondinstrument, sensitive to pressure, is connected to the steam pressuregenerated by the boiler, rather than to the fluid fuel supply line.

Before explaining in detail the present invention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illustrated in the accompanyingdrawings, since the invention is capable of other embodiments and ofbeing practiced or carried out in various ways. Also it is to beunderstood that the phraseology or terminology employed herein is forthe purpose of description and not of limitation, and it is not intendedto limit the invention claimed herein beyond the requirements of theprior art.

In the drawings:

Fig. 1 is a diagrammatic view of my dual control mechanism as adaptedfor-rate of flow control of furnace draft in a stationary installationburning fluid fuel.

Fig. 2 is a diagrammatic view of my dual control mechanism as adaptedfor rateof flow control of furnace draft in a stationary iaistallationburning fluid fuel. 1

Fig. 3 's' a modification of the exhaust valve mechani in, utilizing, adiaphragm chamber.

Fig. 4 is adiagrarfmatic view ofmy' dual .control mechanismas'adapted'for rate of. flow con-. trol of furnace draft in amarine orstationary installation burning solid fuel.

- In Fig. 1 is shown my dual control mechanism adapted to a marineinstallation. I0 represents the mechanism for maintaining adequate andconstant pressure of air for operating the independent pressure systemwhich in turn operates the control valve on the steam line to theblower.

. the rate words, by the differential in pressure in the draft The airis supplied through pipe II and passes into the reservoir -I3 throughreducing valve I2, which is preferably set for 15 pounds pressure. Theair from reservoir I3 passes down the pipe I6 leading to a diaphragmmechanis '20 of the type described in Annin application erial No.463,034 and a flexible branch pipe I'I having a fixed orifice I8bypasses thestream of air. The mechanism III in Fig. 1 differs slightlyfrom the mechanism I0 in Fig. 2, but in operation the two are the same.In Fig. 2 the mechanism is exactly the sameas that disclosed anddescribed in my application, Serial No. 635,356, previously referred to.In mechanism I0 in Fig. 1, IIwrepresents a horsehair or felt strainerthrough which the operating air is passed and which removes all dirt andmoisture from the air. The independent pressure system ordinarilyexhausts to the atmosphere through the exhaust or orifice I9, but iscontrolled by the flapper 56 actuated by of flow of furnace draft or, inother between the stack and air intake duct from the blower. Theindependent pressure is diverted in 25 from increasing. Air

I8 which leads into a central diaphragm chamber 22. A stem 24 abuttingthe top side of the diaphragm chamber 22 forms a valve between pipe I6and chamber 25. A similar stem 25 abutting the bottom side of thediaphragm chamber 22 forms an exhaust valve between the chamber 21 andthe atmosphere. Both chambers are connected on the outside by pipe 28which leads through pipe 29 to the control valve 30. A gauge 3| isconnected to pipe 29 and records the pressure in said pipe. Control.valve 30, which is preferably a diaphragm motor valve, controls'theadmission of steam or other heating medium to the heating tank 36.

'On the closing of exhaust orifice I9, pressure in diaphragm chamber 22builds up, forcing valve 26 closed and valve 24 open, allowing pressurefrom pipe IE to enter directly into chamber 25, flow through connectingpipe 28 into chamber 21 and equalize the pressures therein. Whenpressure in chamber 25 balances the force in central chamber 22, valve24 closes to prevent pressure then flows through pipes 28 and 29 tocontrol valve 30, the pressure of which on the diaphragm 30a. opens thevalve 30 and permits the steam to flow to the pump I02. Valve 30 as hereshown opens on movement down.

Liquid fuel is supplied to the burner I40 through the line I30. Thisfluid fuel may be oil, gas or oil combined with pulverized coal or anyother suitable fluid fuel, but for simplicity the fuel will be spoken ofherein as oil. A pressure responsive instrument (which may be merely aconnection which transmits the original pressure of the oil) is placedin the fuel supply line I30 before the fuel passes to the burner I40,and connects with the helical coil 39, which may be in the form of aBourdon tube or other pressure responsive device. Coil 39 is heldrigidly fixed at one end, and tothe other end of the coil which is freeto move is rigidly attached an arm 40 with a sliding wedge 4| thereonplaced in abutting relation to one end of lever 42 which is fulcrumedabout point 43. (Fulcrum the exhaust valve comprising orifice I 9 andflapper 56, as distinguished from the disclosure in my application,Serial No. 635,356, wherein fulcrum 43 is between the exhaust valve I9and 56 and the sliding wedge 4|.) secured to lever 42. The position ofwedge 4| on arms 40 is adjustable to provide various ranges of control.An instrument I60 responsive to rate of flow is connected in the draftpassage through the boiler. The instrument I60 may be any suitablemechanism, sensitive to rate of flow or a difference in pressure, suchas a mercury manometer, diaphragm or a pair of sylphon bellows.

Herein the instrument I50 comprises a pair of' and is pivoted to one endof arm 53 at the point I68 and on the other end of arm 53 is placed thesliding wedge 54. Arm I69 rests on the top of bellows I6I and is alsopivotally connected to arm 53 at the point I10 between sliding wedge 54and the point I68.

43 this time is outside a Exhaust orifice I9 is rigidly The deviceoperates in the same manner as that disclosed in my application, SerialNo.

635,356, previously referred to, except that the action is transmittedthrough instruments responsive to different characteristics. As pressurein fuel line I30 tends to rise, helical coil 39 unwinds, and actingthrough arm 40 and lever 42 causes orifice I9 to open partially,permitting control valve 30 to partially open, thereby increasing theamount of steam supplied to blower I50, and consequently the amount ofair to take care of the increased amount of fuel being supplied to theburner I40. On a decrease in pressure on the fuel supply line I30, theaction is opposite.

If the draft in the air intake duct -I66 from the blower I50 tends toincrease, this effect is transmitted to the bellows I6I, raising armI69. This elevates-sliding wedge 54 rotating the arm 53 about the pointI68 as a fulcrum so as to cause flapper 56 to partially close nozzle I9.The independent air pressure is then diverted, causing control valve 30to partially close. This reduces the speed of the blower I50sufficiently to maintain a constant draft condition in air intake duct30 and the proper resultant or differential in pressures between airintake duct I66 and the stack I64. If, on the other hand, external windconditions cause the stack draft to decrease (the pressure at the stacknormally being negative), this will cause bellows I62 to contract so asto allow arm I61 to move downwardly, and thereby elevating the wedge 54,with the point I10 now acting as the fulcrum. Flapper 56 is again causedto partially close orifice I3, again diverting the independent pressureto control valve 30, partially closing the same and again reducing thespeed of the blower I50 sufficiently to maintain the constant desireddraft differential between the stack and the air intake -duct I66.

As can be readily seen, this balanced draft system controls the speed ofthe blower I50 so as to provide the required draft differential inaccordance with changes in the fuel oil pressure, and with changes inthe stack draft and the air intake duct pressure. The system is entirelyself-compensating, and the variable factors caused to-counterbalance oneanother so as to prevent over-controlling, which would be noticeable influctuations of the draft differential and consequent CO2 content of thefiue gases. Fluctuations in the pressure and consequent rate of flow ofthe fuel supply are compensated for by changing the speed of the blowerI50, through the action of the independent pressure system operating onthe control valve 30-on the steam supply line 35. The rate of speed ofthe blower I50 is likewise changed from the same independent pressuresystem acting on the'control valve 30 in accordance with the changingdifferential in pressure between the stack draft and the air intakeduct, as caused by external wind conditions. The speed of the blower iscontrolled therefore to provide the proper air supply for completecombustion at all times through the joint and resultant action of thetwo instruments, one being responsive to changes in pressure of the fuelsupply, and the other responsive to changes in the draft through thefurnace. The ratio between the changes in fuel oil pressure and thecorresponding increments of changein the blower speeds is readilyadjusted. Similarly, the sliding wedge 54 may be moved along so as toobtain any desired change of blower speed in relation to an increment ofdraft variation. A In' Fig. 2,'I have shown the same rate of flowcontrol of furnace draft adapted to a stationary installation. Theconstruction and operation of this installation is exactly the sameexcept that the forced draft supplied by the steam-operated blower iseliminated, and the control valve 30 instead of operating the supplyofsteam 'to the blower operates a simple damper mechanism I80, therebycontrolling the draft through the furnace. Also the supply of fuel oilto the burner is iere regulated by the fuel regulator I85, of anysuitable type. The regulator shown herein is actuated by the boiler drumsteam pressure, and it automatically supplies additional fuel oil with adecrease in boiler steam pressure, and vice versa. Therefore, thedesired CO2 content of the flue gas-es is automatically maintained. Themechanism I0 for maintaining a constant and adequate pressure of air foroperating the independent pressure system is shown exactly as thatdisclosed in my application, Serial No. 635,356, and differs slightlyfrom the same mechanism shown in Fig. 1 herein. However, the functionsof the two mechanisms are the same and it is understood that they areinterchangeable. The damper mechanism I80 may be placed in the stack ifdesired, and it should be understood that the forced draft can bedispensed with even in a marine installation.

Again in the stationary installation, the draft control mechanismautomatically maintains the desired draft differential between the airintake duct and the boiler stack by automatically resetting the damperI80. ilt the same time it is so inter-connected that afvariation inpressure or rate of flow of the fuel oil to the burners alsoautomatically resets the damper so as to provide the correct supply ofair for the fuel consumption as varied. Again my draft control mechanism correlates the movement of the damper so as to provide the requireddraft in accordance with the boiler steam pressure, the fuel oil supplypressure, the stack draft and the air intake duct draft. It is entirelyself-compensating, as one condition tends to balance the other, and thisprevents the over-controlling common in other installations.

In Fig. 3, I have shown a modification of the exhaust valve mechanism ofthe independent pressure system, which utilizes a diaphragm chamberinstead of a pair of sylphon bellows. The operation of the diaphragmchamber, however, is exactly the same in effect. Diaphragm chamber 200has a centrally flexible membrane 20I hinged at point 20Ia and dividingthe chamber into two parts, upper chamber 202 and lower chamber 203.Suitable springs or plates should be connected with membrane 20I to makeit incline normally downwardly from the hinge 20Ia, as is well knownin'mechanism of this type. The pipe I63 connects upper chamber 202 tothe stack I64,

and lower chamber 203 connects through pipe I65 to the air intake ductI66 from the blower. A stem 204 extends downwardly through the top ofupper chamber 202 and rests on the membrane 20I. At its upper end stem204 is pivotally attached to lever 42, the fulcrum on 43 (Fig. 1) beingomitted. Lever 42, bearing flapper 56, is fulcrumed therefore atthepoint 205 at the top of stem 204 and at the contact point with slidingwedge 4I, nozzle I9 and the cooperating flapper 56 being intermediatethe two fulcrum points. Therefore, as lever 42 is tilted by either arm40 the steam header of the boiler,

or stem 204, nozzle I9 is partially opened or closed in accordance withthe resultant or diiferential between the movements of arm and stem 204.

Diaphragm chamber 200 operates exactly as the pair of sylphon bellowsIGI and I62 of Fig. 1, the upper chamber 202 corresponding to bellowsI62, and lower chamber 203 corresponding to bellows l6l. The properresultant or diflerential in pressure between air intake duct l 66 andstack I64 is maintained as before, but by using the diaphragm chamber200 in place of the sylphon bellows.

In Fig. 4, I have shown the same rate of flow control of furnace draftadapted to a solid fuel burning installation. The construction andoperationof this installation is similar to that shown in Fig. l, inthat a forced draft is supplied by the steam operated blower I50 but thepressure coil 39 instead of being operated by the pressure of fuel oilis operated by the steam pressure from A steam operated stoker 220 isalso provided for supplying coal or other solid fuel, as needed. Theexhaust valve mechanism of the independent pressure system is shownoperated by a diaphragm chamber 200 as in Fig. 3, but it is understoodthat a pair of sylphon bellows as in Figs. 1 and 2 may be substituted.

The furnace 2l0, of any suitable construction, has steam tubes 2| Itherein, baflies 2I2 to provide a circuitous passage for the burninggases around the steam tubes 2| I, and a stack 2 l3 with adamper 2Mtherein. A steam header 2 l5 0on nects with the pressure coil 39 tooperate the same. The air line 29 from the independent pressure systemnow operates three motor valves 30, preferably of the diaphragm type,one valve 30 operating the damper 21 4 in the stack, another controllingthe supply of steam for operating the blower I50, and the thirdcontrolling the supply of steam operating the stoker 220. The blower I50and stoker 220 may be operated from the same engine if desired. Againthe diaphragm chamber 200 is connected to two different points in thefurnace to register the rate of flow between the two points. The pipeI63, for instance, connects the upper chamber 202 to the point 202:; inthe furnace and pipe I65 connects the lower chamber 203 to the point2030. in the furnace.

The operation of the coal-burning installation is similar to the others.The draftcontrol mechanism automatically maintains the desired draftdifferential between the two points 202a and 203a. in the furnace 2l0 byautomatically resetting the damper 2 l4 and changing the speed of theblower and the stoker. At the same time, it is so interconnected that avariation in the steam pressure generated by the furnace or boiler alsoautomatically resets the damper, blower and stoker so as to increase ordecrease the heat units supplied to the furnace together-with thecorresponding proper supply of air for combustion, as required tomaintain a given pressure of steam in the header 2l5. Again my draftcontrol mechanism correlates the movement of the damper, blower andstoker so as to provide the required draft in accordance with the boilersteam pressure and changes in external draft conditions.

I claim:

1. In a draft control system for a fluid fuel operated furnace, a steamdriven blower for supplying air to the furnace, a'source of steam supplyfor operating the blower, a control valve on the steam supply linecontrolling the supply of steam to said blower, a pilot mechanismutilizing an independent source of pressure for operating said controlvalve and ordinarily exhausting to the atmosphere, an exhaust valvegoverning the exhaust from said pilot mechanism comprising a movableorifice and flapper, levers for moving said orifice and flapper towardand away from each other and so operating the exhaust valve, aninstrument responsive to the pressure of the fuel supply, an instrumentresponsive to the rate of flow of air through said furnace, a

coil actuated by the pressure responsive instrument for moving theorifice lever, an arm actuated by the rate of flow responsive instrumentI 2. In a draft control system for a fluid fuel operated furnace, asteam driven blower for supplying air to the furnace, a, source of steamsupply for operating the blower, a control valve on the steam supplyline controlling the supply of steam to said blower, a pilot mechanismutilizing an independent source of pressure for operating said controlvalve and ordinarily exhausting to the atmosphere, an exhaust valvegoverning the exhaust from said pilot mechanism comprising a movableorifice and flapper, levers for moving said orifice and flapper towardand away from each other and so operating the exhaust valve, aninstrument responsive to the pressure of the fuel supply, a pair ofsylphon bellows responsive to the rate of flow of air through saidfurnace, a helical coil actuated by the pressure responsive instrumentfor moving the orifice lever, an arm actuated by the'difference inpressures between said bellows for moving the flapper lever and soactuating the exhaust valve of the independent pressure system throughthe resultant action of said pressure responsive instrument and pair ofsylphon bellows.

3. In a draft control system for a fluid fuel operated furnace, a dampercontrolling the supply of air to the furnace, a control valve regulatingthe position of said damper, a source of fuel supply for the furnace, apilotmechanism for utilizing an'independent source of pressure foroperating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve governing the exhaust from said pilotmechanism comprising a movable orifice and flapper levers for movingsaid orifice and flapper toward and away from each other and sooperating said exhaust valve, an instrument responsive to pressure ofthe fuel supply, an instrument responsive tothe rate of flow of airthrough said furnace, a coil actuated by the pressure responsiveinstrument for moving the orifice lever, an arm actuated by the rate of'flow responsive instrument for moving the flapper lever and soactuating the exhaust valve of the independent pressure system throughthe resultant action of said governing the exhaust from said pilotmechanism comprising a movable orifice and flapper on'levers for movingsaid orifice and flapper toward and away from each other and sooperating said exhaust valve, an instrument responsive to pressure ofthe fuel supply, a pair of sylphon bellows responsive to the rate offlow of air through said furnace, a helical coil actuated by thepressure responsive instrument for moving the orifice lever, an armactuated by the difference in pressures between said bellows for movingthe flapper lever and so actuating the exhaust valve of the independentpressure system through the resultant action of said pressure responsiveinstrument and pair of sylphon bellows.

5. In a draft control system for a fluid fuel operated furnace, a dampercontrolling the supply of air to the furnace, a control valve regulatingthe position of said .damper, a source of fuel supply for the furnace,automatic means for governing the fuel supplyto the furnace inaccordance with boiler steam pressure, a pilot mechanism for utilizingan independent source of pressure for operating said control valve andordinarily exhausting to the atmosphere, an exhaust valve governing theexhaust from said pilot mechanism, and means responsive to the resultanteffect of pressure of the fuel supply and difference in pressure in saidfurnace at the air intake duct and at the stack for actuating saidexhaust valve.

6. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supply means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaust.

valve governing the exhaust of said pressure to the atmosphere, a supplyand waste valve in said pilot mechanism for supplying and wastingpressure to and from said control valve, diaphragm means in said pilotmeclfanism acted on by said pressure for actuating the supply and wastevalve, and joint means responsive to the resultant effect of thepressure of the fuel and the difference in pressure in said furnace atthe air intake duct and at the stack for actuating said exhaust valve.

7. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supply means, a pilotmechanism utilizing an independent source ofpressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust of said pressure to the atmosphere, a supplyand waste valve in said pilot mechanism for supplying and wastingpressure to and from said control valve, diaphragm means in'said pilotmechanism acted on by said pressure for actuating the supply and wastevalve, an instrument responsive to the pressure of the fuel supply andanother instrument responsive to the difference in pressure in saidfurnace at the air intake duct and at the stack, and joint meansoperated by the resultant action of said instruments for actuating theexhaust valve of the pilot mechanism.

8. In a draft control system for a fluid fuel operated furnace, a steamdriven blower for supplying air to the furnace, a source of steam supplyfor operating the blower, a control valve on the steam supply linecontrolling the flow of steam to said blower, a pilot mechanismutilizing an independent source of pressure for operating said controlvalve governing the exhaust of said pressure to the atmosphereincludingan orifice and flapper, a supply and waste valve in said pilotmechanism for supplying and wasting pressure to and from said controlvalve, a diaphragm chamber in said pilot mechanism acted on by saidpressure for actuating said supply and waste valve, levers for movingsaid orifice and flapper toward and away from each other and sooperating the exhaust valve, an instrument responsive to the pressure ofthe fuel supply, an instrument responsive to the rate of flow of airthrough said furnace, a coil actuated by the pressure responsiveinstrument for moving the orifice lever, an arm actuated by the rate offlow responsive instrument for moving the flapper lever and so actuatingthe exhaust valve of the independent pressure system by the resultantaction of said instruments.

9. In a draft control system for a fluid fuel operatedfurnace, a dampercontrolling the supply of air to the furnace, a control valve regulatingthe position of said damper, a source of fuel supply. for the furnace, apilot mechanism utilizing an independent source of pressure foroperating said control valve governing the exhaust of said pressure tothe atmosphere including an orifice and flapper, a supply and wastevalve in said pilot mechanism for supplying and wasting pressure to andfrom said control valve, a diaphragm chamber in said pilot mechanismacted on by said pressure for actuating said supply and waste valve,levers for moving said orifice and flapper toward and away from eachother and so operating'the exhaust valve, an instrument responsive tothe pressure of the fuel supply, an instrument responsive to the rate offlow of air throughsaid furnace, a coil actuated by the pressureresponsive instrument for moving the orifice lever, an arm actuated bythe rate of flow responsive instrument for moving the flapper lever andso actuating the exhaust valve of the independent pressure system by theresultant action of said instruments. 7

10. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, anindependent pressure system for operating said valve, means forsupplying fuel to the furnace, an instrument responsive to the rate offuel supply, an instrument responsive to the difference in pressure insaid furnace at the air intake duct and in the stack, and means operatedby the resultant action of said instruments controlling the indeplyingmeans. 5

11. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust from said pilot mechanismmeans for supplyingfuel to the furnace and means responsive to the resultant effect of therate of fuel supply and of the difference in pressure in said furnace atthe air intake duct and in the stack for actuating said exhaust valve.

12. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and by the resultant action of said instruments foractuating the exhaust valve of the independent pressure system.

13. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust from said pilot mechanism, means fordiverting said pressure for operating said control valve on the closingof said exhaust valve means for supplying fuel to the furnace, aninstrument responsive to the rate of fuel supply, an instrumentresponsive to the difference in pressure ,in' said furnace at the airintake duct and in the stack, and joint means operated by the resultantaction of said instruments for actuating the exhaust valve of theindependent pressure system.

14. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust from said pilot mechanism, a supply andwaste valve in said pilot mechanism, diaphragm mechanism acted on bysaid pressure for actuating said valve to divert said pressure to thecontrol valve to operate the same on the closing of the exhaust valvemeans for supplying fuel to the furnace, an instrument responsive to therate of fuel supply, an instrument responsive to the diiference inpressure in said furnace at the air intake duct and in the stack, andjoint means operated by the resultant action of said instruments foractuating the exhaust valve of the independent pressure system.

15. In a draft control system for a furnace,

, means for supplying air to the furnace, a control valve governing saidair supplying means, a pilot mechanism utilizing an independent'sourceof pressure for operating said control valve and ordinarily exhaustingto the atmosphere, an exhaust valve governing the exhaust from saidpilot mechanism comprising a relatively movable orifice and flapper,levers for moving said orifice and flapper toward and away from eachother and so operating the exhaust valve means for supplying fluid fuelto the furnace, an instrument responsive to the pressure of the fuelsupply, an instrument responsive to the difierence in pressure in saidfurnace at the air intake duct and in the stack, a coil actuated by thepressure responsive instrument for 'moving the orifice lever, an armactuated by the instrument responsive to the difference in pressure inthe furnace for moving the flapper lever and so actuating the exhaustvalve and the independent pressure system by the resultant action ofsaid instruments.

16. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust from said pilot mechanism, said pilotmechanism including a casing, a pair of diaphragms dividing said casinginto two outer chambers and an inner chamber, a supply valve and awaste, valve in said outer chambers governing the supply waste of saidpressure in said system, said pressure expanding said inner chamber andactuating said supply and waste valves to divert said pressure to thecontrol valve for operating the same on the closing of said exhaustvalve means for supplying fuel to the furnace, and joint meansresponsive to the rate of fuel supply and to the difference in pressurein said furnace at the air intake duct and at the stack for actuatingsaid exhaust valve.

17. In a draft control system for a furnace, means for supplying air tothe furnace, a control valve governing said air supplying means, a pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an exhaustvalve governing the exhaust from said pilot mechanism means forsupplying fuel to the furnace, an instrument responsive to the rate offuel supply, aninstrument responsive to the difference in pressure insaid furnace at the air intake duct and in the stack, said pilotmechanism including a casing, a pair of diaphragms dividing said casinginto two outer chambers and an inner chamber, a supply valve and a wastevalve in said outer chambers governing the supply and waste of saidpressure in said system, said pressure expanding said inner chamber andactuating said supply and waste valves to divert said pressure to thecontrol valve for operating the same on the closing of said exhaustvalve, and joint means operated by the resultant action of saidinstruments for actuating the exhaust valve of the independent pressuresystem.

18. In a draft control system for a solid fuel burning furnace, a steamdriven blower and stoker supplying air and fuel to the furnace, a damperin the stack of said furnace a source of steam supply for operating saidblower, stoker and damper, control valves on the steam supply linecontrolling the supply of steam to said blower, stoker and damper, apilot mechanism utilizing an independent source of pressure foroperating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve' governing the exhaust from said pilotmechanism, means for diverting said pressure for operating said controlvalve on the closing of said exhaust valve, an instrument responsive topressure of the steam generated in the furnace, an instrument responsiveto the difference in pressure in said furnace at the air intake duct andat the stack, joint meansoperating upon the resultant action of saidinstruments for actuating the exhaust valve of the independent pressuresystem.

19. In a draft control system for a solid fuel burning furnace, a steamdriven blower and stoker supplying air and fuel to the furnace, a damperin the stack of said furnace, a source of steam supply for operatingsaid blower, stoker and damper, control valves on the steam supply linecontrolling the supply of steam to said blower, stoker and damper, apilot mechanism utilizing an independent source of pressure foroperating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve governing the exhaust from said pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, a supply andwaste valve in said pilot mechanism for supplying and wasting pressureto and from said control valve, diaphragm means in said pilot mechanismacted on by said pressure for actuating the supply and waste valve, aninstrument responsive to the pressure of steam generated in the furnace,an instrument responsive to the difference in pressure in said furnacebetween the air intake duct and the stack and joint means operated bythe resultant action of said instruments for actuating the exhaust valveof the pilot mechanism,

20. In a draft control system for a solid fuel burning furnace, a steamdriven blower and stoker supplying air and fuel to the furnace, a damperin the stack of said furnace, a source of steam supply for operatingsaid blower, Stoker and damper, control valves on the steam supply linecontrolling the supply of steam to said blower, stoker and damper, apilot mechanism utilizing an independent source of pressure foroperating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve governing the exhaust from said pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, a supply andwaste valve in said pilot mechanism for supplying and wasting pressureto and from said control valve, levers for moving said orifice andflapper toward and away from each other and so operating the exhaustvalve, an instrument responsive to the pressure of steam generated, aninstrument responsive to the difference in pressure in said furnace atthe air intake duct and at the stack, a coil actuated by the pressureresponsive instrument for moving the orifice lever, an arm actuated bythe differential pressure instrument for moving the flapper lever and soactuating the exhaust valve of the independent pressure system by theresultant action of said instruments.

21. In a draft control system for a solid fuel burning furnace, a steamdriven blower and stoker supplying air and fuel to the furnace, a damperin the stack of said furnace, a source of steam supply for operatingsaid blower, stoker and damper, control valves on the steam supply linecontrolling the supply of steam to said blower, stoker and damper, apilot mechanism utilizing an independent source of pressure foroperating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve governing the exhaust from said pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, said pilotmechanism including a casing, a pair of diaphragms dividing said casinginto two outer chambers and an inner chamber, a supply valve and a wastevalve in said outer chambers governing the supply and waste of pressurein said system, said pressure expanding said inner chamber and actuatingsaid supply and waste valves to divert said pressure to the controlvalve for operating the same on the closing of said exhaust valve andmeans responsive to the resultant effect of the pressure of steamgenerated in said furnace and to the difference in pressure in saidfurnace at the air intake duct and the stack for actuating said exhaustvalve.

22. In a draft control system for a solid fuel burning furnace, a steamdriven blower and stoker supplying air and fuel to the furnace, a

damper in the stack of said furnace, a source of steam supply foroperating said blower, stoker and damper, control valves on the steamsupply line controlling the supply of steam to said blower, stoker anddamper, a pilot mechanism utilizing an independent source of pressurefor operating said control valve and ordinarily exhausting to theatmosphere, an exhaust valve governing the exhaust from said pilotmechanism utilizing an independent source of pressure for operating saidcontrol valve and ordinarily exhausting to the atmosphere, an instrumentresponsive to the pressure of steam generated in the furnace, aninstrument responsive to the difference in pressure in said furnace atthe air intake duct and at the stack, said pilot mechanism including acasing, a pair of diaphragms dividing said easing into two outerchambers and an inner chamber, a supply valve and a waste valve in saidouter chambers governing the supply and waste of pressure in saidsystem, said pressure expanding said inner chamber and actuating saidsupply and waste valves to divert said pressure to the controlvalve foroperating the same on the closing of said exhaust valve, and joint meansoperated by the resultant action of said instrument for actuating theexhaust valve of the independent pressure system.

. EDWARD T. DAHL.

